This invention relates to a method of stemming explosive loaded blast holes.
Blasting is used in construction and mining to fragment solid rock so that it can be removed. A number of blast holes are drilled and filled with explosive charges which are detonated to produce shock waves that rupture the surrounding rock. There are a number of parameters that govern the effectiveness of a blast, including geologic structure, the size and spacing of the blast holes, the burden (distance to the free face of the rock surrounding the blast hole), the type, amount, and placement of explosive, the sequence of detonation, and the stemming technique used.
Stemming is the plugging of the blast hole to prevent the escape of blast gasses. This is important because the blast gasses perform the primary work of the blast. If the blast gasses escape, the effectiveness of the blast is diminished, wasting explosive and requiring additional blasting which entails additional risk and increased drilling, labor, and material costs.
An upwardly opening blast hole is typically stemmed with a free-flowing (loose) particulate stemming material, which is poured into the blast hole and then tamped (compacted). Stemming a downwardly opening or horizontal blast hole with free-flowing particulate stemming material, however, is difficult because the stemming material cannot be poured into the hole. Also, the stemming material would gravitate from a downwardly opening blast hole. A downwardly opening or horizontal blast hole may be stemmed with cartridge-type stemming material. However, this procedure is relatively time consuming and expensive. Because of the difficulties associated with stemming downwardly opening or horizontal blast holes, such holes are often not stemmed at all. Thus, the effectiveness of the blast is substantially reduced.